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[Vincenzo Fiorentini <vincenzo.fiorentini@dsf.unica.it>]

I am not an expert on how abinit computes Berry phases,
but I suspect this results is consistent with your
expectation. The Berry phase is defined modulo a lattice
translation (Phys. Rev. B 47, 1651 (1993)), so probably
your number *is* indeed zero in that convention.

best - V. Fiorentini


On 9 Feb 2006, at 2:12 PM, Konstantin Rushchanskii wrote:

> Dear all,
>
> I'm trying to calculate the polarization of a low-symmetry monoclinic
> compound
> Sn2P2S6 (space group Nom. 14), containing the inversion symmetry.
> In this case, the resulting polarization should be zero.
>
> Unfortunately, it is zero only for the ionic part, but not for the
> electron one.
> Electronic Berry phase is exatly equal to 1, and as a result the total
> polarization
> is non-zero.  The input file with simplyfied conditions is given below
> (the case with berryopt -1).
> Moreover, the results are similar also for berryopt 1.
>
> ABINIT identifies the space group correctly.
>
> How can I treat this result?
> Does it mean that the problem is related  to the setting of the
> crystalline structure?
>
> I have found similar problem in the letter of Jian ZHOU (16 Jun 2005),
> but there were no answers to this question.
>
>
> Thank you in advance,
> K.Rushchanskii
>
>
>
> log_file -----------------------------
>  Computing the polarization (Berry phase) for reciprocal vector:
>  0.00000  0.25000  0.00000 (in reduced coordinates)
>  0.00000  0.01766  0.00000 (in cartesian coordinates - atomic units)
>  Number of strings:    16
>  Number of k points in string:    4
>
>  Compute the electronic contribution to polarization
>
>          istr          polberry(istr)
>             1       0.100000000E+01
>             2       0.100000000E+01
>             3       0.100000000E+01
>             4       0.100000000E+01
>             5       0.100000000E+01
>             6       0.100000000E+01
>             7       0.100000000E+01
>             8       0.100000000E+01
>             9       0.100000000E+01
>            10       0.100000000E+01
>            11       0.100000000E+01
>            12       0.100000000E+01
>            13       0.100000000E+01
>            14       0.100000000E+01
>            15       0.100000000E+01
>            16       0.100000000E+01
>         total       0.100000000E+01 (isppol=   1)
>
>  Compute the ionic contributions
> ...
>
>  Summary of the results
>  Electronic Berry phase     1.000000000E+00
>            Ionic phase    -1.221245327E-15
>            Total phase     1.000000000E+00
>    Remapping in [-1,1]     1.000000000E+00
>
>           Polarization     4.567594984E-03 (a.u. of charge)/bohr^2
>           Polarization     2.613338624E-01 C/m^2
>
> log_file -----------------------------
>
>
>
>
> -------------------------
> input.ini
> -------------------------
>
>
> ndtset  2
> nstep 10
>
>
> acell 9.362 7.493 6.55 Angstrom
> angdeg 90 91.2 90
>
> xred
>     0.24310       0.36920       0.95890
>     0.25690       0.86920       0.54110
>     0.75690       0.63080       0.04110
>     0.74310       0.13080       0.45890
>     0.06710       0.39140       0.43940
>     0.43290       0.89140       0.06060
>     0.93290       0.60860       0.56060
>     0.56710       0.10860       0.93940
>     0.26290       0.49750       0.39910
>     0.23710       0.99750       0.10090
>     0.73710       0.50250       0.60090
>     0.76290       0.00250       0.89910
>     0.96720       0.30900       0.17720
>     0.53280       0.80900       0.32280
>     0.03280       0.69100       0.82280
>     0.46720       0.19100       0.67720
>     0.05700       0.19760       0.65580
>     0.44300       0.69760       0.84420
>     0.94300       0.80240       0.34420
>     0.55700       0.30240       0.15580
>
> ntypat 3
> znucl 50 15 16
> natom 20
> typat 1 1 1 1 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3
> nband  54
>
> ngkpt 2  2  2
> ecut 2 Ha
>
>
>   kptopt1   1
>   toldfe1   1.0d-3
>   iscf1   5
>   prtden1 1
>
>   berryopt2 -1
>   rfdir2 0 1 0
>   iscf2 -2
>   kptopt2 1
>   ngkpt2 4 4 4
>   getden2 1
>   tolwfr2 1.0d-4